PROJECT SUMMARY/ABSTRACT HIV and AIDS continue to be devastating health problems, with over 30 million people worldwide infected with the virus, and millions of deaths each year from AIDS. Combination antiretroviral therapy (cART) has greatly decreased morbidity and mortality from AIDS, but the side effects can be severe and the emergence of drug resistance an ongoing challenge. A major obstacle to the cure of this virus has been HIV persistence in reservoirs that contain latently infected resting CD4+ T cells. These cells turn over very slowly, leading to prolonged reservoir persistence despite effective cART, and cessation of antiretroviral therapy invariably leads to virus rebound. The latent viral reservoir thus constitutes one of the major barriers to a sterilizing cure for HIV, and the development of novel, paradigm-shifting approaches will likely be required for successful long- term control. One such novel approach is the use of allogeneic hematopoietic stem cell transplant (allo- HCT) to cure HIV. The promise of this approach is exemplified in the `Berlin patient' who received an allo- HCT from an HIV-resistant CCR5?32 donor, and is the first patient cured of HIV. In addition, there has also emerged provocative data from the two `Boston Patients', who received allo-HCT from CCR5-wildtype donors during continuous cART treatment, and who were able to control viremia for months after therapy interruption. However, virus eventually rebounded, raising concerns that allo-HCT itself, without reconstitution with HIV- resistant T-cells, may be insufficient to eradicate virus. These paired findings raise many critical questions surrounding the mechanisms by which allo-HCT could cure HIV. These questions include (1) Is allo-HCT with HIV-resistant cells a necessary component to the cure? (2) Is there a graft-versus-residual-viral-reservoir (GVRVR) effect, and if so, can this be separated from graft-versus-host disease (GVHD)? and (3) Can an allo- HCT strategy be developed that would make curative transplant available to all HIV+ patients? Given the significant risks associated with allo-HCT, a preclinical model is required. However, until our work, no preclinical model of allo-HCT for HIV eradication existed, and therefore, the creation of this model represented a critical unmet need in the field. During the R21 portion of this grant, we have successfully created this model, and are now poised to use this model to answer fundamental questions about the role that allo- HCT can play in eradication of HIV. We will do this through the following two Specific Aims: (1) We will determine the role of haploidentical allo-HCT and GVHD on the SHIV reservoir. (2) We will determine whether haploidentical allo-HCT using HIV-resistant stem cells expressing the mC46 resistance factor can eradicate the viral reservoir from SHIV-infected recipients. The successful completion of these aims will fundamentally deepen our understanding of the cellular and immunologic components of the viral reservoir, and will establish novel transplant?based strategies for HIV eradication.